This question tests your understanding of verb tenses and causative structures in English grammar. Let's analyze the sentence: "Susan _____ the mechanic _____ her car yesterday."

Step 1: Identify the time reference
The word "yesterday" clearly indicates that this action happened in the past.

Step 2: Understand causative structures
When someone arranges for another person to do something for them, we use causative verbs like "have," "get," or "make." The correct structure is:

Subject + have/had + object + base form of verb

Step 3: Apply the correct tense
Since the action happened yesterday, we need the past tense form "had" instead of "has" (present) or "having" (continuous form).

Step 4: Complete the structure
After "had + object (the mechanic)," we need the base form of the verb "repair" (not "to repair").

Final Answer: The correct option is "had / repair" because it follows the past tense causative structure: Subject (Susan) + had + object (the mechanic) + base verb (repair).

Related Grammar Concepts

Causative Verbs: These are verbs that indicate one person causes another to perform an action. Common causative verbs include have, get, and make.

Past Simple Tense: Used for completed actions in the past, often with time markers like "yesterday," "last week," or specific past dates.

Important Formula

Causative structure with "have":
Subject + have/had + person + base form of verb + object

Example: I had my brother fix my computer.